I thought I'll pick up on Lou's post but create a new topic so it's easier for people to find. here the original post:

Lou Jost wrote:

Quote:

would actually nice to have identical wafers spread out over forum members so that tests could be done to compare lenses across continents

This really would be an excellent idea. Why don't we act on it? Find one with really fine detail (preferably with those nice resolution test patterns on it) and either buy dupes and sell to others on the forum to recover costs, or cut one into pieces with a glass cutter and send the pieces to others.

Robert, I'd love to split or buy a duplicate wafer with you. Do you have duplicates of one with a fine test pattern? Or could you choose a source for a given known-good type which has multiple copies, so we could all buy one?

I'm in if we find some at reasonable prices (the larger ones seem to have gotten quite expensive).

So far I could only find sources which send random copies and those I got are not really fine enough to judge things like moire.

maybe we could use some small ones, not so good to judge flat field, but easier to find in large quantities, cheaper and also better for shipping.

This can be done, yeah. I have a box of cut wafer chips, one of which I used in my recent tests, its fine structures makes a decent target for CA and sharpness testing. I have 2 trays, a total of 100 of them. The person I bought it from has even more.

I'm planning to photograph them all and let the forum decide on the best target to use.

As for specific CA and distortion tests, I can get a bunch of those misroscopy calibration targets from Taobao, they are cheap, decent quality. There are gridded ones that work well for distortion testing.

From that, we simply need to standardise our lighting to make results completely consistent. There's not a lot of us doing these tests anyway, so one tray of good silicon chips fitting the criteria will do. These chips can be put in an envelope and posted for very cheap prices._________________Personal Flickr page: https://www.flickr.com/photos/133023063@N04/Blog still under construction

A calibrated test pattern like those would be very useful, but they don't look like they get fine enough.

The transparent ones have a huge advantage over wafers: lighting from below is much easier to standardize than lighting from above, and short working distances don't cause problems with that kind of lighting, so the results would not be confounded with effects of working distance on lighting angles._________________Lou Jost
www.ecomingafoundation.wordpress.comwww.loujost.com